Shaggy Mane mushrooms are one of the easy-to-identify species. Beginners can't really get in trouble with this if they are paying attention. The top picture is what the mushroom should look like when you collect them- a tall (about 3-4 inches tall) oval with shaggy, curled edges- sort of like old shingles- on the outer layer. This appearance also gives it the common name of Lawyer's Wig.

The scientific name is Coprinus comatus, and it is one of the strange self-digesting mushrooms. This will give you the means to positively identify it. This also means that if you find some, don't go back another day to collect it, because it will be unusable, if not gone. The black parts are not poisonous, but the good flavor is ruined.

mature shaggy mane mushroom (photo by jhy)

As the cap opens out you can see that it is already turning black, and there are stringy threads "flowing" down the outside. At this point it's way too late to eat. However, this appearance, coupled with the tall oval shape of the young mushrooms, will guarantee that you've found the correct species.

It grows in lawns and waste places, and you may see fruiting bodies from spring through fall. I've usually seen them from August onwards, but they can appear earlier. Avoid eating mushrooms that are growing in soil that is polluted- for example, a brownfield. The only real lookalike is Coprinopsis veriegata (also known as Coprinus variegatus and Coprinus quadrifidus and Coprinus ebulbosus. Taxonomy is in real flux with DNA testing.) The lookalike tends to grow on logs, not from the ground, and is not as white. It is also edible, so this is not a deadly mistake, but some references say to not consume alcohol with the lookalike.

self-digested shaggy mane mushroom (photo by jhy)

These Shaggy Manes are almost completely gone. The self-digestion process has continued until there is only a tiny cap left, and strings of the black "ooze."

Collect the white, shaggy ovals, and use right away. They will self-digest even after picking, sometimes within a few hours.

If you find a place where they grow, visit it each year because the underground mycelium will keep sending up the fruiting bodies (the part you see) annually.